In recent years, people with diabetes have typically measured their blood glucose level by lancing a finger tip or other body location to draw blood, applying the blood to a disposable test strip in a hand-held meter and allowing the meter and strip to perform an electrochemical test of the blood to determine the current glucose concentration. Such discrete, in vitro testing is typically conducted at least several times per day. Continuous in vivo glucose monitoring devices are currently being developed to replace in vitro devices. Some of these continuous systems employ a disposable, transcutaneous sensor that is inserted into the skin to measure glucose concentrations in interstitial fluid. A portion of the sensor protrudes from the skin and is coupled with a durable controller and transmitter unit that is attached to the skin with adhesive. A wireless handheld unit is used in combination with the skin-mounted transmitter and sensor to receive glucose readings periodically, such as once a minute. Every three, five or seven days, the disposable sensor is removed and replaced with a fresh sensor which is again coupled to the reusable controller and transmitter unit. With this arrangement, a person with diabetes may continuously monitor their glucose level with the handheld unit. Detailed descriptions of such a continuous glucose monitoring system and its use are provided in U.S. Pat. No. 6,175,752, issued to Abbott Diabetes Care, Inc., formerly known as TheraSense, Inc., on Jan. 16, 2001, which is incorporated by reference herein in its entirety.
Portable insulin pumps are widely available and are used by diabetic people to automatically deliver insulin over extended periods of time. Currently available insulin pumps employ a common pumping technology, the syringe pump. In a syringe pump, the plunger of the syringe is advanced by a lead screw that is turned by a precision stepper motor. As the plunger advances, fluid is forced out of the syringe, through a catheter to the patient. Insulin pumps need to be very precise to deliver the relatively small volume of insulin required by a typical diabetic (about 0.1 to about 1.0 cm3 per day) in a nearly continuous manner. The delivery rate of an insulin pump can also be readily adjusted through a large range to accommodate changing insulin requirements of an individual (e.g., various basal rates and bolus doses) by adjusting the stepping rate of the motor. In addition to the renewable insulin reservoir, lead-screw and stepper motor, an insulin pump includes a battery, a controller and associated electronics, and typically a display and user controls. A typical insulin pump has a footprint about the size of a deck of cards and can be worn under clothing or attached with a belt clip. A disposable infusion set is coupled with the pump to deliver insulin to the person. The infusion set includes a cannula that is inserted through the skin, an adhesive mount to hold the cannula in place and a length of tubing to connect the cannula to the pump.
The continuous glucose monitoring and insulin delivery systems described above include various drawbacks. The rigid, flat mounting surfaces of the skin-mounted transmitters currently being developed can make them uncomfortable to wear. Additionally, since these transmitter units do not conform to the portion of the body they are mounted to, adherence to the skin and the locations on the body available for use can be limited. Currently available insulin pumps are complicated and expensive pieces of equipment costing thousands of dollars. The overall size and weight of the insulin pump and the long length of infusion set tubing can make currently available pumping systems cumbersome to use. Additionally, because of their cost, currently available insulin pumps have an intended period of use of up to two years, which necessitates routine maintenance of the device such as recharging the power supply and refilling with insulin.
Various attempts to significantly miniaturize and combine the monitoring and pumping systems described above while making them more reliable, less complex and less expensive have not been successful. Constraints which hinder such development efforts include the system requirements of sensors, insulin supplies and batteries which require periodic replacement, and the need to reduce risk of infection, increase user comfort and ease of use.